Cellulose dissolving solvent, cellulose dissolving method, and method for producing cellulose molded body

Abstract

To provide a solvent which can dissolve cellulose uniformly in a short time at around room temperature without needing a special pretreatment and moisture control, a dissolution method for cellulose using the solvent, and a manufacturing method for a cellulose molding.SOLUTION: A dissolution solvent for cellulose of the present invention includes a tetraalkylammonium hydroxide, water, and dimethyl sulfoxide. For the concentration of each solvent, the concentration of the tetraalkylammonium hydroxide is 2.0-25 wt.%, the concentration of water is 1.0-35 wt.%, and the concentration of the dimethyl sulfoxide is 40-97 wt.%. And, by adding cellulose to the cellulose dissolution solvent and stirring at room temperature until the solution becomes transparent, a cellulose dissolution solution can be obtained, and by using the cellulose dissolution solution, a cellulose molding can be manufactured.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a solvent used for dissolving cellulose, and a method for producing a molded article using the solvent. [Background technology]

[0002] The applicant has filed a patent application for a mixture of tetraalkylammonium acetate (TAAA) and an aprotic polar solvent as a solvent for dissolving cellulose (Patent Document 1). However, the solvent of Patent Document 1 has a large effect of water on its cellulose solubility. When about 5 wt% of water is contained, the solubility of cellulose is significantly reduced. However, since the solvent is highly hygroscopic, waterproofing management is strict in the series of processes from the solvent to the cellulose solution. Furthermore, water is often used as a coagulating liquid when spinning the cellulose solution or forming a film. After the coagulating liquid is used, it is common to distill off the water and recover and reuse only the cellulose solvent. Both TAAA and aprotic polar solvents have strong interactions with water molecules, so when the moisture content falls below a certain value, it is not easy to remove the moisture. Therefore, long-term distillation is required while using a vacuum and heat in combination. As a result, TAAA and aprotic polar solvents decompose, and large amounts of energy are consumed by distillation. The solubility of cellulose decreases when TAAA and aprotic polar solvents decompose. As a result, the number of times the cellulose solvent is recycled decreases. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2012-211302 A Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides a solvent capable of uniformly dissolving cellulose at about room temperature in a short period of time without requiring special pretreatment or moisture control, a method for dissolving cellulose using the solvent, and a method for producing a cellulose molded body. [Means for solving the problem]

[0005] As a result of extensive investigations aimed at achieving the above object, the present inventors have completed the invention described below. [1] A solvent used to dissolve cellulose, The solvent comprises a tetraalkylammonium hydroxide represented by the following formula, water, and dimethyl sulfoxide: The concentration of each of the solvents in the solvent is within the ranges of 2.0 to 25 wt % for tetraalkylammonium hydroxide, 1.0 to 35 wt % for water, and 40 to 97 wt % for dimethyl sulfoxide. [ka] In the formula, R1, R2, R3 and R4 each independently represent an alkyl group having 1 to 4 carbon atoms. [2] The solvent according to [1], wherein the tetraalkylammonium hydroxide comprises at least one of tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide. [3] A method for dissolving cellulose, comprising contacting cellulose with the solvent according to [1] or [2] above to dissolve the cellulose. [4] A method for producing a cellulose molded body, comprising the steps of: producing a cellulose molded body by using a cellulose dissolving solution obtained by the method for dissolving cellulose according to [3] above. Effect of the Invention

[0006] The solvent of the present invention is capable of dissolving cellulose uniformly in a short period of time without any special pretreatment, regardless of the crystalline form of cellulose.

[0007] In addition, compared to the solvent of Patent Document 1, the solubility of the solvent of the present invention does not decrease even when it contains 30% water, so that severe distillation and concentration conditions are not required for handling in the dissolving step or recycling the solidification liquid, and therefore decomposition of solvent components such as DMSO is avoided. In addition, high energy is not used in the step of recycling the solidification liquid.

[0008] Furthermore, a solution in which cellulose is dissolved in the solvent of the present invention has fluidity even at room temperature and has excellent moldability. [Brief description of the drawings]

[0009] [Figure 1] Photographs of the cellulose solutions prepared in Examples 1, 2, 3, 6, and 7 (the magnetic stirrer used for stirring can be seen in some of the photographs. The same is true for Figures 2 and 4.) [Diagram 2] Photographs of the cellulose spinning process and the resulting cellulose fibers obtained in Example 1 [Diagram 3] UV spectra of the cellulose solutions prepared in Examples 2-4 and 7-9 [Figure 4] Photographs of the cellulose solutions prepared in Examples 4, 8 and 9 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The tetraalkylammonium hydroxide, which is a component of the cellulose dissolving solvent of the present invention, is not limited in any way as long as it is a tetraalkylammonium hydroxide of the chemical formula shown in the above [1], and may be used alone or in combination of two or more kinds. Specific examples of the compounds include the following compounds. Examples of the hydroxide include tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, methyltripropylammonium hydroxide, methyltributylammonium hydroxide, ethyltripropylammonium hydroxide, ethyltributylammonium hydroxide, propyltributylammonium hydroxide, dimethyldipropylammonium hydroxide, dimethyldibutylammonium hydroxide, diethyldipropylammonium hydroxide, diethyldibutylammonium hydroxide, and the like. More preferred are tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), and tetrabutylammonium hydroxide (TBAH). Particularly preferred are tetraethylammonium hydroxide and tetrapropylammonium hydroxide.

[0011] The tetraalkylammonium hydroxide (TAAH) used in the present invention to dissolve cellulose is water-soluble and is readily available as a commercially available chemical in aqueous solution. The cellulose dissolving solvent of the present invention contains tetraalkylammonium hydroxide (TAAH), water, and dimethyl sulfoxide (DMSO), and therefore TAAH can be mixed in the form of an aqueous solution with DMSO to form a dissolving solvent.

[0012] The cellulose dissolving solvent of the present invention is composed of TAAH, water and DMSO, and the composition ratio is adjusted to be within the concentration range of 2.0 to 25 wt% TAAH, 1.0 to 35 wt% water, and 40 to 97 wt% DMSO, more preferably, 2.0 to 22 wt% TAAH, 3.0 to 30 wt% water, and 50 to 95 wt% DMSO. A TAAH concentration lower than 2 wt% is undesirable because of its low solubility and dissolution rate, while a TAAH concentration higher than 25 wt% is undesirable because of its low solubility and dissolution rate, and because the cellulose solubility decreases when the concentration is higher than 25 wt%. In addition, the cellulose may decompose during dissolution or when the resulting cellulose solution is stored.

[0013] A water concentration of less than 1.0% is not preferred because the solubility of cellulose decreases and the TAAH becomes unstable and may decompose, whereas a water concentration of more than 35% is not preferred because the solubility of cellulose decreases.

[0014] The solvent of the present invention may contain other organic solvents in addition to tetraalkylammonium hydroxide, water, and dimethylsulfoxide. Examples of such organic solvents include alcohol, N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, and pyridine. The addition of these solvents can improve the dissolution of cellulose and adjust the viscosity and reactivity of the cellulose solution.

[0015] The method for preparing the cellulose dissolving solvent of the present invention is not particularly limited. For example, a cellulose solvent can be obtained by preparing a commercially available TAAH aqueous solution to a desired concentration, adding DMSO thereto, and stirring. If the TAAH concentration of the commercially available TAAH aqueous solution is lower than the desired concentration when the water concentration is in the optimal range, it is preferable to distill it before use and concentrate it to the desired moisture content before use. If the concentration is higher than the desired concentration, water is added to dilute it before use. There is no particular limit to the temperature when mixing, and room temperature is sufficient.

[0016] The method of dissolving cellulose in the cellulose dissolving solvent of the present invention is not particularly limited. For example, a cellulose solution is prepared by adding cellulose to a predetermined amount of the cellulose dissolving solvent of the present invention and stirring until a transparent solution is obtained. Stirring may be performed with a commonly used mechanical stirrer. For a beaker scale, stirring with a magnetic stirrer is sufficient. The temperature during dissolution may be 10 to 80°C, and dissolution may be performed at room temperature without temperature adjustment. If the temperature is lower than 10°C, the solubility or dissolution rate of cellulose is low, which is not preferable. If the temperature is higher than 80°C, the cellulose, TPAH, or TEAH may decompose or be decomposed, which is not preferable. More preferably, the temperature is 15 to 70°C, and most preferably, the temperature is 20 to 60°C.

[0017] The amount of cellulose dissolved is not particularly limited. It may be adjusted appropriately depending on the degree of polymerization (molecular weight) of cellulose and the application. For example, it is 1 to 20 wt%. If the amount of cellulose dissolved is too low, the productivity will be low. On the other hand, if the amount of cellulose dissolved is too high, it is not preferable because the cellulose may be incompletely dissolved, the uniformity of the solution may decrease, and the fluidity of the obtained cellulose solution may be lost.

[0018] The cellulose to be dissolved in the cellulose solvent of the present invention is not particularly limited. Examples of the cellulose to be dissolved include wood pulp, cotton, cotton linter pulp, cellulose powder, bacterial cellulose, sea squirt cellulose, and bagasse cellulose, regardless of the crystal structure, degree of crystallization, and degree of polymerization of the cellulose.

[0019] The cellulose solution obtained by dissolving cellulose in the cellulose dissolving solvent of the present invention is degassed and used as a molding solution. There is no particular limitation on the molding method, but a wet molding method can generally be applied. For example, the cellulose solution is sucked into a syringe, a nozzle is attached to the syringe pump or a microfeeder, and the cellulose solution is discharged from the nozzle into a water bath at room temperature while moving the syringe, and the fiber is washed and then wound up by a winder to prepare cellulose fiber. When forming a cellulose film, for example, a cellulose solution is cast onto a glass substrate, and the liquid film is washed while being coagulated by immersion in a coagulating liquid such as water or alcohol, and then dried to prepare a film. EXAMPLES

[0020] The present invention will be further described with reference to examples, although the present invention is not limited to these examples.

[0021] (Materials and solvents used) Cellulose pulp: NBKP pulp (Canfor) and cotton linter pulp were used, both of which were obtained from Marubeni Corporation. Absorbent cotton: purchased from Nacalai Tesque. 40% tetrapropylammonium hydroxide aqueous solution: manufactured by Tokyo Chemical Industry Co., Ltd. 55% tetrapropylammonium hydroxide aqueous solution: Obtained by concentrating a 40% Tokyo Chemical Industry Co., Ltd. product. 35% tetraethylammonium hydroxide aqueous solution: manufactured by Tokyo Chemical Industry Co., Ltd. 56% tetraethylammonium hydroxide aqueous solution: Obtained by concentrating a 35% Tokyo Chemical Industry Co., Ltd. product. Other reagents were purchased from Nacalai Tesque.

[0022] (Measurement of visible light transmittance) The cellulose solution was sandwiched between two glass slides and measured using a UV-visible spectrophotometer UV-visible transmission spectrum chart to evaluate the visible light transmittance at a wavelength of 450 nm. The device used for the measurement was Shimadzu UV-36003000, and the measurement wavelength range was 400 nm to 800 nm. The thickness of the liquid film of the cellulose solution was 10 μm.

[0023] (Viscosity measurement of cellulose solution) The viscosity of the cellulose solution was measured using a vibration viscometer (VISOCOMATE MODEL VM-10A series) manufactured by Sekonic Corporation, and the measurement temperature was room temperature set at 23°C.

[0024] [Example 1] 0.25g of 40% tetrapropylammonium hydroxide (TPAH) aqueous solution and 4.75g of dimethyl sulfoxide were added to a 10ml vial, and 0.1g of linter pulp was added and dissolved while stirring with a magnetic stirrer at room temperature. The appearance of the solution was observed at regular intervals, and the point at which the cellulose became a uniform, transparent solution was taken as the point at which the cellulose was completely dissolved, and the dissolution time was measured. The measured dissolution time and the results of the color and transmittance of the obtained cellulose solution are shown in Table 1. A photograph of the appearance of the cellulose solution is shown in Figure 1.

[0025] The obtained cellulose solution was drawn into a syringe and discharged into a distilled water bath at room temperature using a nozzle with a pore diameter of 0.5 mm, while stretching the fibrous transparent gel. Next, the fibrous transparent gel was washed with distilled water to remove tetrapropylammonium hydroxide and dimethylsulfoxide, and air-dried at room temperature to obtain cellulose fibers. A photograph of the obtained cellulose fibers is shown in Figure 2.

[0026] [Examples 2 to 12] The weights of the components shown in Table 1 were weighed, and the cellulose was dissolved and evaluated in the same manner as in Example 1. The results are shown in Table 1 and Figures 1, 3 and 4. All of the obtained cellulose solutions were transparent.

[0027] [Comparative Examples 1 to 5] The weight of each component shown in Table 1 was weighed, and the cellulose was dissolved and evaluated in the same manner as in Example 1. The results are shown in Table 1. No transparent cellulose solution was obtained in any case.

[0028] The dissolution conditions and evaluation results of Examples 1 to 12 and Comparative Examples 1 to 5 are summarized in Table 1, and the composition ratios of the solvents are shown in Table 2.

[0029] [Table 1]

[0030] As shown in Table 1, in Examples 1 to 12, cellulose was not pretreated and cellulose was able to be completely dissolved uniformly and in a short time at room temperature. On the other hand, cellulose could not be dissolved in Comparative Examples 1 to 5. The viscosities of the cellulose solutions prepared in Examples 5, 8, 9, and 12 were high and exceeded the measurement range of the vibration viscometer (1000 mPa.s or less), so they could not be measured.

[0031] [Table 2] [Industrial Applicability]

[0032] As described above, the cellulose dissolving solvent of the present invention can dissolve cellulose uniformly in a short time, regardless of the degree of polymerization and crystalline form of cellulose, and does not require the conventional strict waterproofing and water content control processes and operations. Furthermore, the cellulose-containing solution dissolved in the solvent of the present invention has excellent fluidity and moldability, and can be widely applied to the technical field of manufacturing cellulose molded bodies. In addition, the cellulose-containing solution dissolved in the solvent of the present invention can also be applied to the synthesis of acylated cellulose derivatives such as cellulose acetate because of its basicity.

Claims

1. A solvent used to dissolve cellulose, The solvent consists of a tetraalkylammonium hydroxide represented by the following formula, water, and dimethyl sulfoxide, The concentration of each of the solvents in the solvent is within the ranges of 2.0 to 25 wt % for tetraalkylammonium hydroxide, 1.0 to 35 wt % for water, and 40 to 97 wt % for dimethylsulfoxide. 【Chemistry 1】 In the formula, R1, R2, R3 and R4 each independently represent an alkyl group having 1 to 4 carbon atoms.

2. 2. The solvent of claim 1, wherein the tetraalkylammonium hydroxide comprises at least one of tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

3. A method for dissolving cellulose, comprising contacting cellulose with the solvent according to claim 1 or 2 to dissolve the cellulose.

4. A method for producing a cellulose molded body, comprising the steps of: producing a cellulose molded body by using a cellulose dissolving solution obtained by the method for dissolving cellulose according to claim 3 .

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