JP6933056B2 - Manufacturing method of cellulose nanofiber powder - Google Patents

Description

The present invention relates to a method for producing cellulose nanofiber powder. More specifically, the present invention relates to a method for producing a cellulose nanofiber powder having excellent dispersibility in water and an organic solvent.

Cellulose nanofibers (hereinafter referred to as CNF) are mainly obtained by mechanically and / or chemically defibrating pulp in an aqueous medium, and are cellulose fibers having a thickness on the order of nanometers and a high aspect ratio. be.
Although CNF is as light as 1/5 of iron, it is 5 times stronger than iron, has a low coefficient of thermal expansion, and has the characteristics that the elastic modulus does not change from low temperature to high temperature. Therefore, composite materials using CNF are expected to be lightweight, high strength, low coefficient of thermal expansion and resistant to temperature changes.
Further, since CNF is a natural material, it is environmentally friendly, can be incinerated, and has the advantages of being cheaper than carbon nanofibers. Further, CNF has various excellent characteristics, and various applications have been developed by utilizing the characteristics.

However, the dried CNF dispersed in water does not restore the state before drying even if water is added to the dried solid because hydrogen bonds are formed between the fine cellulose fibers. Therefore, CNF is produced in a state of being dispersed in water and used for various purposes in a wet state without being dried. The dispersion concentration of CNF in water is generally about 1 to 20%. For example, when it is combined with a resin, a large amount of water needs to be removed.

Further, when pulp is defibrated in a resin, the resin generally has a high viscosity and requires strong mechanical force or heating, so that deterioration such as coloring is likely to occur. In addition, since CNF chemically defibrated by oxidation treatment has high hydrophilicity, surface treatment is required to remove the catalyst and oxidizing agent or to disperse the highly hydrophilic CNF in a hydrophobic resin. It is a material that is difficult to handle industrially.

In order to improve these problems, a method for obtaining a CNF solid having the same redispersibility as before drying has been investigated, and the pH of the aqueous suspension of CNF is adjusted to 9 to 11, and then dehydrated and dried. A method for producing a dry solid of CNF (Patent Document 1), a dry solid of CNF (Patent Document 2) in which 5 to 300% by weight of a water-soluble polymer is contained in CNF and dried, and CNF and hydroxy acids are used. CNF-containing dried products containing CNF (Patent Document 3) and the like have been studied.
Further, in the chemically modified CNF, even if it is once dried, the chemically modified CNF dispersion is obtained by drying as a method of easily nano-dispersing in a solvent as in the case of preparing from an undried state. After treating the dried solid of CNF with hot water, the CNF dispersion dispersed in a solvent (Patent Document 4) and the cellulose oxide fiber were defibrated to obtain a CNF dispersion, and then a reaction containing a reducing agent. CNF dispersions that reduce in liquid (Patent Document 5) and the like have been studied.

JP-A-2017-8175 Japanese Unexamined Patent Publication No. 2017-8176 Japanese Unexamined Patent Publication No. 2017-2138 JP-A-2017-2136 Japanese Unexamined Patent Publication No. 2017-2135

However, in the method for obtaining a CNF solid in the above prior art document, additives other than CNF remain in the solid, so that the purity of CNF is lowered, and it is necessary to perform chemical denaturation again.

In view of the above situation, it is an object of the present invention to provide a method for producing CNF powder having excellent dispersibility in water or an organic medium by a simple operation.

As a result of diligent studies to solve the above problems, the present inventor has produced a CNF powder that solves the above problems by mixing ammonium carbonate with the CNF aqueous dispersion and then decomposing sodium carbonate by heating. We have found what we can do and have completed the present invention.

That is, the first invention of the present invention is a method for producing CNF powder having the following steps (a) to (c).
(A) A step of obtaining a mixed dispersion of a CNF aqueous dispersion and ammonium carbonate.
(B) A step of drying the mixed dispersion to obtain a dry solid of CNF and ammonium carbonate.
(C) A step of heating the dry solid to decompose ammonium carbonate to obtain CNF powder.

The second invention is the method for producing a CNF powder according to the first invention, wherein in the mixed dispersion liquid in the step (a), ammonium carbonate is 30 to 100 parts by mass with respect to 1 part by mass of CNF.

The third invention is the method for producing CNF powder according to the first invention or the second invention, wherein the drying temperature in the step (b) is 20 to 50 ° C.

Further, in the fourth invention, in the step (c), after crushing the dry solid obtained in the step (b), the obtained pulverized product is heated to decompose sodium carbonate. The method for producing CNF powder according to any one of the inventions.

The fifth invention is the method for producing a CNF powder according to the fourth invention, wherein the size of the pulverized product is 1 to 250 μm.

Further, the sixth invention is the method for producing CNF powder according to any one of the first to fifth inventions, wherein the heating temperature in the step (c) is 50 to 150 ° C.

According to the production method of the present invention, CNF powder having excellent dispersibility in water and organic media and having a large specific surface area can be obtained. Therefore, the CNF powder obtained by the production method of the present invention is mixed with various resins and the like. By doing so, an excellent composite material can be produced.

An optical micrograph (magnification of 400 times) of the dispersion of the cellulose powder containing CNF obtained in Example 1 on the polycarbonate diol is shown. An optical micrograph (magnification of 400 times) of the dispersion of the cellulose powder containing CNF obtained in Example 2 in ethylene carbonate is shown. The photograph of the dispersion in the solid polycarbonate diol obtained in Comparative Example 1 is shown. The photograph of the dispersion in the solid ethylene carbonate obtained in Comparative Example 1 is shown.

The CNF in the present invention is not particularly limited, and examples thereof include those obtained by nano-izing a raw material mainly composed of cellulose, for example, pulp, natural cellulose, regenerated cellulose, etc. by chemical or mechanical defibration treatment. It is a cellulose fiber containing fine fibers having a fiber width of nano size.
Further, the CNF in the present invention may contain cellulose before being defibrated, but for the purpose of the present invention, it is preferable that the CNF contains as little as possible other than CNF.

Hereinafter, the steps (a) to (c) in the production method of the present invention will be described in detail.
(1) Step (a) is a step of obtaining a mixed dispersion of a CNF aqueous dispersion and ammonium carbonate.
The CNF aqueous dispersion is one in which the CNF is dispersed in water or a mixed solution containing water, and examples of the mixed solution containing water include a mixed solution such as alcohols having good miscibility with water. It is preferable to disperse it in water alone. As the CNF aqueous dispersion, a commercially available CNF aqueous dispersion having a cellulose concentration of 0.1 to 20% by mass can be used as it is.

Ammonium carbonate may be mixed in the form of powder or in the state of an aqueous solution having an appropriate concentration. From the viewpoint of ease of handling, it is preferable to mix in a powder state.
The method of adding ammonium carbonate is not particularly limited, and examples thereof include a method of adding ammonium carbonate in several times, a method of adding powder and an aqueous solution separately, and the like.
If the concentration of the CNF aqueous dispersion before mixing with ammonium carbonate is low, ammonium carbonate may be mixed in the powder state, but if the concentration is high and the semi-solid state is used, the mixing operation is performed by using an aqueous ammonium carbonate solution. Becomes easier.

In the step of obtaining the mixed dispersion liquid, it is preferable to use a stirrer suitable for mixing the slurry in order to prevent reaggregation of CNF and uniformly disperse the mixture. Examples of the stirrer include a rotation / revolution stirrer, a ball mill, a disc mill, a roll mill, and the like, and among these, it is preferable to use a ball mill and a disc mill.

In the mixed dispersion, ammonium carbonate is preferably mixed at a ratio of 30 to 100 parts by mass, more preferably 40 to 80 parts by mass, with respect to 1 part by mass of CNF in the dispersion. If it is less than 30 parts by mass, the concentration of the mixed dispersion becomes high, so that it becomes difficult to pulverize after drying in the next step, and cellulose in the dried product easily reaggregates. If it exceeds 100 parts by mass, a large excess of carbon dioxide is used. It is inefficient because it removes ammonium.
Further, it is efficient in terms of workability of slurry mixing that the water concentration in the dispersion liquid is 30 to 90% by mass. If the water concentration exceeds 90% by mass, the energy use increases due to drying in the step (b), and if it is less than 30% by mass, the slurry concentration increases and workability such as stirring deteriorates.

The liquid temperature at the time of mixing ammonium carbonate is not particularly limited, but is preferably 10 to 30 ° C. from the viewpoint of handling. If the liquid temperature exceeds 50 ° C., sodium carbonate may be decomposed, which is not preferable.

(2) Step (b) is a step of drying the mixed dispersion of CNF and ammonium carbonate to obtain a dry solid of CNF and ammonium carbonate.
The drying method is not particularly limited, and known methods such as natural drying, heat drying, vacuum drying, freeze drying and spray drying can be used. Among these, heat drying and vacuum drying are preferable.

Since ammonium carbonate thermally decomposes at 58 ° C., it is preferable to maintain the drying temperature at 20 to 50 ° C. in order to remove water while suppressing thermal decomposition. If the temperature is lower than 20 ° C, the drying will be slower, and if the temperature exceeds 50 ° C, the thermal decomposition of ammonium carbonate will proceed more easily.

When the moisture is removed by drying, the dried solid matter becomes lumpy. Therefore, in order to efficiently carry out the thermal decomposition in the subsequent step, it is preferable to pulverize the dried solid matter. The size of the particles after pulverization is preferably 1 to 250 μm, more preferably 1 to 100 μm.
The size of the crushed particles shall be classified by a sieve having a mesh size of 1 to 250 μm.
When the particles of the dry solid are crushed to less than 1 μm, the cellulose fibers are likely to be cut, and when it exceeds 250 μm, the efficiency of thermal decomposition is deteriorated and the dispersibility of the finally obtained CNF powder is lowered.

For crushing the dry solid, a crusher such as a ball mill, a disc mill, or a rotor mill can be used. For example, when the ultracentrifugal crusher ZM200 manufactured by Lette Co., Ltd. is used, it is possible to prevent the formation of CNF having a reduced aspect ratio due to excessive fine pulverization by using a screen having an opening of 80 μm.

(3) Step (c) is a step of heating the dry solid material to decompose ammonium carbonate to obtain CNF powder.
Ammonium carbonate can be thermally decomposed by heating the dry solid material which has been pulverized and passed through a sieve as needed to obtain a cotton-like bulky CN powder.
The heating temperature for decomposing ammonium carbonate is preferably 50 to 150 ° C. Within this range, the thermal decomposition of ammonium carbonate is likely to proceed, and the cellulose is not colored.

The CNF powder produced by the steps (a) to (c) may be mixed with a reactive material such as (meth) acrylic monomer, polyol or epoxy resin to be used as a raw material for polyester, polyurethane, acrylic resin or the like. It can be directly mixed with a thermoplastic resin such as polyethylene or polypropylene or a composition such as a paint or an adhesive to form a composite material. As a method for mixing, a known method for producing a composite material by mixing CNF and a resin can be applied.
If necessary, the composite material may contain other additives, and examples of the additives include antioxidants, ultraviolet absorbers, antioxidants, fillers, colorants, and fortifiers. Examples thereof include mold release agents, flame retardants, thermoplastic resins, surfactants, catalysts, stabilizers and pigments.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.
<Example 1>
50 g of ammonium carbonate and 50 g of water were mixed to prepare a 50% by mass ammonium carbonate aqueous solution.
50 g of the ammonium carbonate aqueous solution was added to 100 g of a CNF aqueous dispersion (concentration 5% by mass) manufactured by Mori Machinery Co., Ltd., and the mixture was stirred and mixed at 1800 rpm for 5 minutes using a spin-rotation revolving stirrer ARE-310 manufactured by Shinky Co., Ltd. Further, 50 g of the ammonium carbonate aqueous solution was added, and the mixture was mixed with the rotation / revolution stirrer for 5 minutes.
Next, 250 g of ammonium carbonate powder was added and mixed with the rotation / revolution stirrer for 15 minutes to obtain a slurry containing CNF and ammonium carbonate.
The obtained slurry was spread thinly on a vat and vacuum dried at 40 ° C. for 2 days to obtain a solid in which CNF was dispersed in ammonium carbonate.
The obtained solid was pulverized with a high-speed crusher Wonder Blender WB-1 manufactured by Osaka Chemical Co., Ltd. for 5 minutes to obtain a powder that passed through a sieve having a mesh size of 20 μm. Further, the solid remaining on the sieve was repeatedly pulverized and sieved by WB-1 to obtain a powder that had passed through the entire sieve.
The obtained powder is finally heated at 100 ° C. for 10 hours while gradually raising the temperature from 60 ° C. in a vacuum dryer to thermally decompose ammonium carbonate to obtain 4 cotton-like bulky powders. I got .97g. Table 1 shows the results of measuring the specific surface area of the obtained CNF powder by the BET method.

<Example 2>
The same operation as in Example 1 was carried out except that 250 g of ammonium carbonate powder was added to 100 g of a CNF aqueous dispersion (concentration: 5% by mass) manufactured by Mori Machinery Co., Ltd. to obtain 4.90 g of a cotton-like bulky powder. .. Table 1 shows the results of measuring the specific surface area of the obtained CNF powder by the BET method.

<Comparative example 1>
A CNF aqueous dispersion (concentration: 5% by mass) manufactured by Mori Machinery Co., Ltd. was spread thinly on an aluminum cup as it was, and dried at a temperature of 100 ° C. The obtained dried product was a thin paper-like solid. Table 1 shows the results of measuring the specific surface area of the obtained solid by the BET method.

<Evaluation of dispersibility in water>
The CNF aqueous dispersion (concentration 5% by mass) manufactured by Mori Machinery Co., Ltd. and the powder obtained in Example 1 were each diluted to 1% by mass with water, and then using the ultrasonic dispersion processing device UP400S manufactured by Heelscher Co., Ltd. After treatment at 50 ° C. for 20 minutes, the E-type viscometer TVE-22H manufactured by Toki Sangyo Co., Ltd. and the rotor No. Using No. 1, the viscosity was measured under the conditions of 100 rpm and 25 ° C.
As shown in Table 2, the viscosity of the CNF powder obtained in Example 1 is almost the same as that of CNF manufactured by Mori Machinery Co., Ltd., and it can be seen that the CNF powder is excellent in dispersibility in water.

<Dispersibility in solvents and resins>
Table 3 shows the results of dispersing the solids obtained in Examples 1, 2 and Comparative Example 1 using ethylene carbonate as a solvent and polycarbonate diol T-6001 manufactured by Asahi Kasei Chemicals Co., Ltd. as a resin.
The powder obtained in Example was uniformly dispersed in ethylene carbonate and polycarbonate diol, whereas the solid obtained in Comparative Example 1 remained mostly paper-like and had poor dispersibility. The photographs showing the dispersibility of each are shown in FIGS. 1 to 4.

The abbreviations in Table 3 are as follows.
EC: Ethylene carbonate PCD: Polycarbonate diol T-6001

Claims (6)

A method for producing cellulose nanofiber powder, which comprises the following steps (a) to (c).
(A) A step of obtaining a mixed dispersion of cellulose nanofiber aqueous dispersion and ammonium carbonate.
(B) A step of drying the mixed dispersion to obtain a dry solid product of cellulose nanofibers and ammonium carbonate.
(C) A step of heating the dry solid to decompose ammonium carbonate to obtain cellulose nanofiber powder. The method for producing cellulose nanofiber powder according to claim 1, wherein in the mixed dispersion liquid in the step (a), ammonium carbonate is in a ratio of 30 to 100 parts by mass with respect to 1 part by mass of the cellulose nanofibers. The method for producing cellulose nanofiber powder according to claim 1 or 2, wherein the drying temperature in the step (b) is 20 to 50 ° C. The cellulose nano according to any one of claims 1 to 3, wherein in the step (c), the dry solid obtained in the step (b) is crushed, and then the obtained pulverized product is heated to decompose sodium carbonate. Method for producing fiber powder. The method for producing cellulose nanofiber powder according to claim 4, wherein the size of the pulverized product is in the range of 1 to 250 μm. The method for producing cellulose nanofiber powder according to any one of claims 1 to 5, wherein the heating temperature in the step (c) is 50 to 150 ° C.

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