JP2003261712A - Cellulose-dissolving solvent and method for preparing cellulose solution - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solvent readily dissolving natural cellulose and regenerated cellulose under mild conditions of normal temperatures and pressures, and to provide a method for preparing a cellulose solution. <P>SOLUTION: The solvent comprises an inorganic salt and hydrazine. This solvent enables cellulose to be dissolved in high concentrations independently of its crystal form, not only for naturally-occurring cellulose I but also for cellulose II prepared by mercerization of the natural cellulose and cellulose III prepared by treating the natural cellulose with an amine. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD [0001] The present invention does not require any special pretreatment to treat natural cellulose and regenerated cellulose at room temperature.
The present invention relates to a cellulose-soluble solvent that can be easily dissolved at normal pressure and a method for preparing a cellulose solution using the same. INDUSTRIAL APPLICABILITY The method for preparing a cellulose-soluble solvent and a cellulose solution of the present invention is widely used for molding cellulose materials such as fibers and films.

[0002]

2. Description of the Related Art Cellulose is the most abundant organic substance on earth and is the main constituent of wood. It is a naturally occurring large amount of recycled resources and biodegradable polymer. Currently, it has been used for textiles, paper, films, etc. as the largest application, but since it has very poor meltability and solubility, it is difficult to mold it when handling it as a material,
Its use is extremely limited. If a new solvent for cellulose having an extremely high solubility is newly found, it can be expected to solve these problems, and a wide variety of applications other than the above-mentioned applications will be possible.

Solvents that have been conventionally used include
Amine aqueous solution of copper, cobalt, zinc, etc. (E. Schweize
r, J. Prakt. Chem., 72, 109 (1857), G. Jayme, Papi
er, 5,244 (1951), G. Jayme and K. Neuschaffer, Nau
turwissenschften, 42, 536 (1955).), but industrial use is declining due to the recovery process and cost of heavy metals that cause environmental pollution.

The viscose method (CF Cross, ET Bevan, and C. Beadl), which is the mainstream of the current cellulose fiber production,
e, Ber., 26, 1090-1097 (1893).), the cellulose is once modified by a chemical change to develop the solubility as a cellulose derivative, and after being fiberized, it is returned to the original cellulose, which is an extremely complicated process. Be forced. Such a liquid that is dissolved by a chemical reaction is not originally defined as a solvent. In addition, there is a defect that hydrogen sulfide gas, which is highly toxic, is generated as a by-product of the manufacturing process using toxic carbon disulfide, and an alternative method is strongly desired.

As a cellulose solvent found in recent years, there is a mixture of lithium chloride and dimethylacetamide (C.
L. McCormick and DK Lichatowich, J. Polym. Sc
i.: Polym. Lett. Ed., 17, 479-484 (1979).). However, depending on the type of cellulose to be dissolved, the cellulose suspension dispersed in the solvent may be heated to 100 ° C. or higher, or
Pretreatment such as preliminarily swelling cellulose in water or alcohol for a long time is required. Further, since expensive lithium salt is used, it is limited to use on a laboratory scale and has not been industrialized yet.

The only cellulose solvent that has been industrially put to practical use other than the above-mentioned viscose method is the N-methylmorpholine-N-oxide / water system (DL Johnso
n, US Patent 3,447,939, (1969).). The solvent is 130
Cellulose will not dissolve unless heated to around ℃
Always dangerous because it is explosive at 0 ° C. Also,
Dissolved cellulose rapidly decomposes in such a high temperature range, and an additive for preventing it is indispensable.

In addition, it has long been known that when a concentrated aqueous solution of an inorganic salt is heated to around 100 ° C., cellulose is dissolved. The types of inorganic salts are calcium thiocyanate, magnesium thiocyanate, zinc chloride, etc., but energy consumption is large because heating is required at high temperature, and molecular chain scission of cellulose is avoided at high temperatures as described above. However, it is disadvantageous in obtaining a high-strength cellulose fiber.

Recently, it has been invented that a high-concentration sodium thiocyanate aqueous solution dissolves cellulose (Japanese Patent Laid-Open No. 8-158148). However, this solvent system does not dissolve natural type cellulose, but only type II type cellulose treated with an aqueous sodium hydroxide solution, or amorphous cellulose that is not in a crystalline state. Further, heating at 100 ° C. or higher is still required, and from the viewpoint of the above molecular chain scission, there is a factor that the strength is lowered as compared with cellulose before dissolution.

[0009]

As can be seen from the characteristics of the cellulosic solvents found so far, the conventional ones derivatize the cellulose with a chemical reaction or heat it to a high temperature range of 100 ° C or higher. If not, most of them do not exhibit solubility. Considering the cost on an industrial scale, there is currently no solvent that avoids these two points. A solvent system that solves these problems and is capable of molding a cellulose material having excellent mechanical properties such as strength from a cellulose solution dissolved under mild conditions is required.

The present invention has been made in view of the above circumstances, and an object thereof is a cellulose-soluble solvent capable of easily dissolving natural cellulose and regenerated cellulose under mild conditions of normal temperature and normal pressure, and It is to provide a method for preparing a cellulose solution.

[0011]

[Means for Solving the Problems] In an existing aqueous solution system in which water is used as a medium, attention is paid to the fact that heating to 100 ° C. or higher is required to dissolve cellulose. It was judged that the action and the solubility were too low. The present invention solves the above problems by using hydrazine (NH ₂ NH ₂ ) having a strong swelling action instead of water.

The cellulose-soluble solvent according to the present invention is a cellulose-soluble solvent which dissolves natural cellulose and regenerated cellulose under conditions of normal temperature and normal pressure, and is characterized by comprising an inorganic salt and hydrazine.

According to the above-mentioned cellulose-soluble solvent, it is possible to dissolve cellulose at a high concentration without depending on the crystal form of cellulose. In addition, the above-mentioned cellulose-soluble solvent is not limited to naturally occurring type I cellulose, but also has a high concentration for type II cellulose prepared by mercerization and type III cellulose prepared by treatment with amines. Cellulose can be dissolved.

In the cellulose-soluble solvent according to the present invention, the inorganic salt is preferably any of thiocyanate, sodium iodide and potassium iodide. The thiocyanate is preferably any one of sodium thiocyanate, potassium thiocyanate and lithium thiocyanate.

The method for preparing a cellulose solution according to the present invention is characterized in that natural cellulose or regenerated cellulose is dissolved in a cellulose-soluble solvent composed of an inorganic salt and hydrazine at room temperature and atmospheric pressure.

In the method for preparing a cellulose solution according to the present invention, a liquid is obtained by dissolving an inorganic salt in hydrazine having a strong swelling action. Cellulose is dispersed in this liquid to promote the diffusion of cellulose to prepare a uniform cellulose solution under the conditions of normal temperature and normal pressure.

In the method for preparing a cellulose solution according to the present invention, the inorganic salt is preferably any of thiocyanate, sodium iodide and potassium iodide. The thiocyanate is preferably any one of sodium thiocyanate, potassium thiocyanate and lithium thiocyanate.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. The cellulose-soluble solvent according to the embodiment of the present invention overcomes the above problems by using hydrazine having a strong swelling action instead of water. That is,
Sodium thiocyanate (NaSCN) as an inorganic salt is dissolved in hydrazine until saturated to give a colorless liquid. Instead of sodium thiocyanate, potassium thiocyanate (KSCN), lithium thiocyanate (LiS
A thiocyanate such as CN) may be used, or a part of an alkali halide such as sodium iodide (NaI) or potassium iodide (KI) may be used. Cellulose is dispersed in this, and it is stirred by a stirrer, or shear stress is applied by a roller-shaped material to promote the diffusion of cellulose and obtain a uniform cellulose solution at room temperature.

It should be noted here that the conventional aqueous solution of the inorganic salt did not dissolve the cellulose unless it was heated to 100 ° C. or higher, whereas if hydrazine was used as the medium instead of water, it was easily obtained even at room temperature. To dissolve. Since it dissolves easily at room temperature in this way, it does not cause a decrease in the molecular weight due to cleavage or decomposition of the cellulose molecular chain, and does not require a large-scale heating device or energy. Therefore,
Cost reduction is possible. Table 1 shows the solubility of natural type cellulose I having a degree of polymerization of 210 at 25 ° C.

[0020]

[Table 1]

Regarding the relationship between the hydrazine / salt ratio and the solubility of cellulose, the solubility of cellulose increases as the salt concentration increases in all cases. That is, a saturated solution as shown in Table 1 dissolves cellulose best. The minimum concentration of the salt required to develop the solubility of cellulose is 38%, 34%, 5% in lithium thiocyanate, sodium thiocyanate, and potassium thiocyanate, respectively.
A weight ratio of 4% is required.

The solvent system found according to the present invention dissolves cellulose in high concentrations independent of the crystalline form of cellulose. Table 1 shows only naturally occurring type I, but the type II cellulose prepared by mercerization and the type III cellulose prepared by treating with amines also show the same dissolving power. . For the preparation of the cellulose solution, Table 1
In the case of using the above cellulose, it takes several hours for a low concentration of less than 5%, about 3 days for up to about 10%, and about 5 days for obtaining the maximum solubility. This is because the solution itself becomes so viscous that the cellulose being dissolved is less likely to diffuse. Considering that the dissolution of cellulose is relatively quicker than other solvent systems and that no pretreatment of cellulose such as swelling step or heating is required, the dissolution step is extremely simple and low in cost. Therefore, it can be said that the solvent is very suitable for large-scale preparation.

Table 2 shows the relationship between the degree of polymerization and the solubility of cellulose in the hydrazine / sodium thiocyanate system. The solubility of cellulose in this solvent depends on the degree of polymerization of cellulose. Solubility decreases with the degree of polymerization as seen with other macromolecules; for example, in the hydrazine / sodium thiocyanate system, as shown in Table 2, DP210 cellulose gives up to 18% solution, while DP376, DP536 , DP716 and 14%, 10% and 9% as the degree of polymerization increases.

[0024]

[Table 2]

The cellulose-soluble solvent according to the present embodiment is one in which cellulose is so-called physically bound to the solvent to exhibit a dissolving power. Therefore, if the solvent is removed from the cellulose solution in which the cellulose is dissolved, the cellulose is easily regenerated, and neither decomposition nor chemical reaction of the cellulose occurs. Therefore, by using this solvent, it is possible to mold into a material that utilizes the essence of cellulose. This is judged from the infrared absorption spectrum of cellulose regenerated from the cellulose solution.

The solution in which cellulose is dissolved is poured into a non-cellulosic solvent such as water or alcohol and well stirred to remove hydrazine and thiocyanate. At this time, the cellulose is solidified and converted into a solid. As described later, there is a close relationship between the coagulant and the solid crystal structure of regenerated cellulose. A coagulant that dissolves well hydrazine and an inorganic salt and that has regenerated cellulose having a rigid crystal structure is desirable.

The regenerated cellulose was filtered, washed well with ion-exchanged water, dried overnight at 60 ° C., and the infrared absorption spectrum was measured. As a result, no absorption other than cellulose was observed. It can be seen that the deterioration of the cellulose accompanied by the chemical reaction did not occur.

Further, even when the cellulose solution in which the cellulose is dissolved in the cellulose-soluble solvent according to the present embodiment is stored for a long period of time, the cellulose is hardly decomposed. For example, in a solvent of 100 mL of hydrazine / sodium thiocyanate shown in Table 1, cellulose of DP210 0.10
When 0 g is dissolved, the specific viscosity of the solution, which is one of the measures of the molecular weight of cellulose, is 1.17, and the specific viscosity of the solution left at room temperature for 1 month is 1.16. That is, the decrease in the molecular weight due to decomposition is very small even after being left for 1 month as compared with immediately after the dissolution.

The intrinsic viscosity [η] of the solution obtained by varying the concentration of cellulose was 1.64 for the cellulose solution before dissolution and 1. for the cellulose solution left at room temperature for 1 month.
The molecular weight reduction rate was 51, which was less than 8% with respect to the cellulose of DP210. On the other hand, the molecular weight reduction rate of cellulose in the currently industrialized N-methylmorpholine-N-oxide / water system is about 30% even if the stabilizer is added, and therefore the cellulose dissolution according to the present embodiment is It can be said that the organic solvent is a solvent in which the degradability of cellulose is extremely low.

The cellulose regenerated from the cellulose solution dissolved in the present solvent system has a type II crystal structure when water is used as the coagulant. By the wide-angle X-ray diffraction method, the diffraction angle 2θ =
Peaks appear at 12.3 °, 20.2 °, 21.9 °,
It is completely consistent with cellulose II produced by mercerization. When coagulated with methanol or 2-butanol, a broad peak appears with a small intensity at a diffraction angle 2θ = 20 °, and amorphous cellulose is produced. When regenerated cellulose is used as a fiber or film, it is desirable that the cellulose molecular chains form tight hydrogen bond stitches with each other in order to obtain high strength. Therefore, it is better to use water that produces type II as a coagulant.

The cellulose solution dissolved in the present solvent system becomes anisotropic when the cellulose concentration is around 8% and forms a liquid crystal phase. However, gelation also progresses at a concentration of about 5%. These concentrations largely depend on the molecular weight of the dissolved cellulose and the dissolution temperature, and change depending on the type of salt. Specific examples are shown below.

For example, FIG. 1 shows the relationship between the temperature of the cellulose solution and the cellulose concentration when the cellulose of DP210 is dissolved using a saturated solution of hydrazine / sodium thiocyanate. In this case, gelation starts at a concentration of 5% as shown in FIG. However, the gelation rate at this concentration is extremely slow as long as the temperature is 10 ° C. or lower, and the gel formation rate is extremely slow. After that, the gelling temperature and speed gradually increase as the cellulose concentration increases,
20 in the hydrazine / sodium thiocyanate system
Above 0 ° C., no gel is formed at any cellulose concentration. Since the gel generated at 20 ° C or lower is also thermoreversible, it is immediately dissolved when heated to 20 ° C or higher and returns to a fluid state with a fluidity.

Further, in the temperature range where the concentration of cellulose is 8% or more and the gel is not formed, the solution becomes anisotropic and the anisotropy of the cellulose solution appears. This becomes noticeable as the concentration of cellulose increases. The anisotropic phase can be confirmed by a polarization microscope, and birefringence which is not seen in the isotropic phase is observed.

So far, liquid crystal phases have been found by using some cellulose solvents, but all of them are expressed only at a relatively high concentration of 10% or more.
That is, in sodium thiocyanate / hydrazine, cellulose is expected to have a fairly rigid rod-like structure, and the molecules are oriented with each other even at a low concentration. It is known that spinning with such a liquid crystal solution gives fibers with very high strength and high elastic modulus. For example, high-strength aromatic polyaramid fiber (trade name: Kevlar) is produced by this liquid crystal spinning method (SL Kwolek,
PW Morgan, WR Sorenson, US Patent 3,063,966 (1
962)). Further, not only fiberization but also molding of other cellulosic materials from a liquid crystal solution is extremely advantageous for producing a product having excellent mechanical strength.

The present invention is not limited to the above-mentioned embodiment, but can be implemented with various modifications.

[0036]

As described above, according to the present invention, there is provided a method for preparing a cellulose-soluble solvent and a cellulose solution capable of easily dissolving natural cellulose and regenerated cellulose under mild conditions of normal temperature and normal pressure. You can

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a temperature of a cellulose solution and a cellulose concentration when DP210 cellulose is dissolved in a saturated solution of hydrazine / sodium thiocyanate, which is an example of a cellulose-soluble solvent according to an embodiment of the present invention. is there.

Claims (6)

[Claims] 1. A cellulose-soluble solvent which dissolves natural cellulose and regenerated cellulose under conditions of normal temperature and normal pressure, wherein the cellulose-soluble solvent comprises an inorganic salt and hydrazine. 2. The cellulose-soluble solvent according to claim 1, wherein the inorganic salt is any one of thiocyanate, sodium iodide and potassium iodide. 3. The thiocyanate is any one of sodium thiocyanate, potassium thiocyanate and lithium thiocyanate.
The cellulose-soluble solvent described in 1. 4. A method for preparing a cellulose solution, which comprises dissolving natural cellulose or regenerated cellulose in a cellulose-soluble solvent consisting of an inorganic salt and hydrazine under conditions of normal temperature and normal pressure. 5. The method for preparing a cellulose solution according to claim 4, wherein the inorganic salt is any one of thiocyanate, sodium iodide and potassium iodide. 6. The thiocyanate is any one of sodium thiocyanate, potassium thiocyanate and lithium thiocyanate.
The method for preparing a cellulose solution according to 1.