JP2000204195A - Hydroxypropylcellulose having low substitution degree - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydroxypropylcellulose having a low substitution degree, capable of giving a solution state which is excellent in transparency and stable in a wide temperature range, by controlling the amount of the substituted hydroxypropyl groups. SOLUTION: This hydroxypropylcellulose having a low substitution degree has an average substituted hydroxypropyl group content of 0.1-0.4 mole per glucose unit. Therein, the glucose units each substituted by two or more moles of the hydroxypropyl groups are contained in an amount of <=5% based on the number of all the glucose units, and the transmittancy of a solution containing the hydroxypropylcellulose in a concentration of 2 wt.% in a 10 wt.% sodium hydroxide aqueous solution is >=90% at 10-50 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-substituted hydroxypropylcellulose showing stable solubility and high solution transparency in an aqueous alkaline solution over a wide temperature range.

[0002]

2. Description of the Related Art Hydroxypropylcellulose is composed of 3 units of glucose unit (C ₆ H ₁₀ O ₅ ) which is a structural unit of cellulose.
A nonionic polymer in which individual hydroxyl groups are etherified with a hydroxypropyl group and have various useful properties, and are therefore used in a wide range of fields. The properties of hydroxypropylcellulose vary greatly depending on the amount of hydroxypropyl group substitution. As a method of expressing the degree of substitution, the average number of moles of substituents per glucose unit (M
The method represented by S) is the most common and widely used.

[0003] Hydroxypropylcellulose having a high degree of substitution, having an average substitution mole number of 2 to 3, is soluble in cold water, insoluble in hot water, and soluble in organic solvents such as alcohol.
Those having a low degree of substitution do not dissolve in water or organic solvents, but swell when contacted with water and have the property of dissolving in an aqueous alkali solution such as alkali hydroxide. Due to these properties, low-substituted hydroxypropylcellulose is used as a disintegrant or binder for pharmaceuticals, and is used as a thickener for alkaline solutions.

[0004] Examples of low-substituted hydroxypropylcellulose include JP-B-48-38858 and JP-B-57-38858.
No. 53100 discloses a production method in which the average number of moles of substituted hydroxypropyl groups per glucose unit is 0.05 to 1.0. However, those produced by these methods are soluble in an alkaline aqueous solution, but contain many undissolved components, so that the transparency of the solution was low. In addition, since their solubility in an alkaline aqueous solution varies greatly depending on the temperature,
There has been a problem that use conditions are limited in applications requiring stability of the solution.

[0005]

The solubility of low-substituted hydroxypropylcellulose in an aqueous alkali solution is as follows:
It is greatly affected by the degree of hydroxypropyl group substitution. In order to obtain a low-substituted hydroxypropylcellulose exhibiting good solubility, the amount of substitution of hydroxypropyl groups is controlled, that is, the average number of moles of substituted hydroxypropyl groups per glucose unit, which is a structural unit thereof, and the number of hydroxypropyl groups The ratio of substituents having different numbers of moles of substitution is important. By controlling the substitution amount of the hydroxypropyl group in this way, the appearance of a low-substituted hydroxypropylcellulose that is excellent in solution transparency and provides a stable solution state in a wide temperature range has been desired, but has been sufficiently satisfactory. There is nothing to do yet.

[0006]

Means for Solving the Problems The present inventors have made intensive studies to solve the above problems, and as a result, have found that glucose units (C
₆ H ₁₀ O ₅₎ average molar substitution of hydroxypropyl groups per is in a low-substituted hydroxypropyl cellulose of 0.1 to 0.4, the number of glucose units substituted with 2 or more moles of hydroxypropyl groups 90% or less of light transmittance at 10 ° C. to 50 ° C. in a solution having a concentration of 5% or less based on the total number of glucose units and a concentration of 2% by weight with respect to a 10% by weight aqueous sodium hydroxide solution. The low-substituted hydroxypropylcellulose characterized by the above is soluble in an alkaline solution, exhibits high transparency, and finds that the solution state is stable under a wide range of temperatures,
The present invention has been accomplished.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The low-substituted hydroxypropylcellulose of the present invention, which will be described in more detail below, has an average number of moles of substituted hydroxypropyl groups per glucose unit of 0.1 to 0.4. When the average substitution mole number is lower than 0.1, the solution becomes opaque due to undissolved substances when dissolved in an alkaline solution, and when it exceeds 0.4, the solution becomes cloudy and all become opaque solutions.

The low-substituted hydroxypropylcellulose of the present invention has a hydroxypropyl group-substituted mole number of 2
It is preferable that the number of the substituted products (glucose units) is 5% or less based on the total number of glucose units.
If the ratio of the substituted product having 2 or more hydroxypropyl group substitutions exceeds 5%, the solution becomes cloudy and becomes an opaque solution as described above. This is because the transparency of the solution is lost due to an increase in the ratio of the unsubstituted compound having low solubility in an alkali solution and the substituted compound having a hydroxypropyl group substitution mole number of 2 or more.

In the production of the low-substituted hydroxypropyl cellulose of the present invention, in the first step, the cellulose is reacted with an alkali hydroxide to produce an alkali cellulose. As a method for preparing the alkali cellulose, a method in which the raw pulp is immersed in an aqueous alkali hydroxide solution and then squeezed to remove an excess aqueous alkali hydroxide solution to obtain a desired alkali cellulose composition is suitable.

The cellulose used as a raw material includes wood pulp, linter pulp and the like, and there is no limitation depending on the shape such as a sheet-like cellulose, a pulverized one, and any one can be used. . As the alkali hydroxide aqueous solution, an aqueous solution of sodium hydroxide, potassium hydroxide, lithium hydroxide or the like is used, and sodium hydroxide is preferable. The concentration of the aqueous alkali hydroxide solution is preferably 20 to 45% by weight, particularly preferably 30 to 40% by weight. If the concentration of the aqueous alkali hydroxide solution is lower than 20% by weight, the swelling of the cellulose is insufficient and the cellulose is not activated, and the subsequent etherification reaction does not proceed sufficiently. Meanwhile, 4
If the content exceeds 5% by weight, the composition of the prepared alkali cellulose becomes non-uniform, the solubility in an alkaline solution varies depending on the temperature, and the temperature change of the solution physical properties becomes large.

Other methods for preparing alkali cellulose include a method of mixing pulp with an aqueous solution of alkali hydroxide in a dispersion medium such as an organic solvent and a method of directly spraying an aqueous solution of alkali hydroxide on pulp. The composition is non-uniform as compared with alkali cellulose obtained by immersion in an aqueous solution, and is unsuitable for producing a low-substituted hydroxypropylcellulose having a desired alkali solution solubility.

The alkali hydroxide in the alkali cellulose plays an important role as a catalyst for the reaction of propylene oxide, and also has a role to increase the reactivity of the cellulose and activate it. On the other hand, the moisture in the alkali cellulose reacts with the propylene oxide to produce impurities that must be removed from the product, which is undesirable. Therefore, in order to effectively produce low-substituted hydroxypropylcellulose by the reaction of alkali cellulose and propylene oxide, it is necessary to control the amount of alkali hydroxide and the amount of water in the alkali cellulose during the preparation of the alkali cellulose. is there.

In the production of the low-substituted hydroxypropylcellulose of the present invention, the amount of alkali hydroxide and the amount of water in the alkali cellulose are 0.1 to 1.0, especially 0.2 in weight ratio to the cellulose. To 0.8, and the water content is preferably 0.1 to 2.0, particularly preferably 0.3 to 1.0. When the amount of alkali hydroxide and the amount of water are smaller than the above range, the reaction does not proceed sufficiently, and when the amount of alkali hydroxide and the amount of water are larger than the above range, propylene oxide is preferably reacted with water. In this case, a desired amount of hydroxypropyl group is not obtained, and a large amount of effort is required to remove by-produced impurities. It becomes difficult to control the amount of group substitution. Therefore, as a method for preparing an alkali cellulose which is the first step in the production of the low-substituted hydroxypropylcellulose of the present invention, the raw pulp is immersed in an aqueous alkali hydroxide solution and then squeezed to remove excess alkali hydroxide aqueous solution. The method of making the composition of the alkali cellulose is preferable.

In the second step in the production of the low-substituted hydroxypropylcellulose of the present invention, the alkali cellulose and propylene oxide are sufficiently mixed and reacted. The reaction temperature is 30 to 80 ° C, especially 40 to 70 ° C. Preferably, the reaction is carried out by adding propylene oxide in a molar ratio to cellulose of 0.15 to 2.0. Reaction temperature is 30 ° C
When the temperature is lower than 80 ° C., it is not practical because the reaction progresses extremely slowly and the reaction proceeds for a long time. When the temperature is higher than 80 ° C., the number of moles of substituted hydroxypropyl groups in hydroxypropyl cellulose is 2 or more. Generation ratio increases,
The amount of impurities generated by the reaction between propylene oxide and water increases, which is not preferable. If the amount of propylene oxide is out of the range, a predetermined amount of hydroxypropyl group substitution cannot be obtained.

As a method for adding propylene oxide, a method in which a predetermined amount of propylene oxide is added all at once,
Any method such as adding several times or adding continuously can be carried out. This reaction can also be carried out using an organic solvent having low reactivity with propylene oxide as a dispersion medium.

Although the reaction product of the present invention contains impurities and the like resulting from the reaction of alkali hydroxide or propylene oxide with water, the reaction product can be easily purified by a known method and contains no impurities and has a high purity. Obtained as low-substituted hydroxypropylcellulose.

The substituted composition of the low-substituted hydroxypropylcellulose obtained by the present invention can be determined by a known method, for example, the method described in Carbhydro. Res., Vol . 170 , p. 207 (1987). it can. For example, a method for measuring the composition of a substituted product is as follows: a low-substituted hydroxypropylcellulose in which a free hydroxyl group is methylated by reacting with a methylating agent such as iodomethane in the presence of an alkali is subjected to acid decomposition with trifluoroacetic acid or the like, followed by reduction. To obtain a sorbitol derivative. If the acetylated product using acetic anhydride or the like is subjected to gas chromatography, those having different hydroxypropyl group substitution numbers and substitution positions can be separated, and their ratios can be determined.

The transparency of the low-substituted hydroxypropylcellulose obtained by the present invention can be judged by the light transmittance. The light transmittance refers to the transmittance of a low-substituted hydroxypropylcellulose solution under the same conditions assuming that the light transmittance of purified water measured using a photoelectric colorimeter is 100.
The measuring method is specifically described in Examples.

[0019]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. (Example 1) (1) Production of low-substituted hydroxypropylcellulose 100 parts by weight of sheet pulp was immersed in a 40% by weight aqueous sodium hydroxide solution to absorb the aqueous solution of sodium hydroxide into the pulp, and then 3 kg / cm. The mixture was pressurized to ² to remove excess sodium hydroxide aqueous solution, and the weight ratio of alkali hydroxide to cellulose and cellulose was adjusted to 0.55 and 0.90, respectively, by weight ratio to cellulose. The prepared alkali cellulose was pulverized, put into a pressurized reactor equipped with an internal stirrer, and sufficiently purged with nitrogen. Then, 24 parts by weight of propylene oxide (molar ratio to cellulose: 0.67) was charged, and The reaction was performed at a temperature of 3 ° C. for 3 hours. The reaction product was neutralized with acetic acid to remove residual sodium hydroxide, and then washed with warm water at 50 to 60 ° C. It was blow-dried at 80 ° C to obtain 108 parts by weight of a low-substituted hydroxypropylcellulose as a colorless solid. The average number of moles of substituted hydroxypropyl groups determined by the Zeisel method was 0.26.

(2) Substituted composition 3 parts by weight of the low-substituted hydroxypropylcellulose obtained in (1) were dissolved in 250 parts by weight of dimethyl sulfoxide. After adding 30 parts by weight of powdery sodium hydroxide to this solution, 100 parts by weight of methyl iodide was added with stirring and reacted at 60 ° C. for 4 hours. The reaction product was poured into 10000 parts by weight of hot water to precipitate methylated hydroxypropylcellulose. The precipitate is collected and collected at 70 ° C for 6 hours.
Dried for hours. To 5 parts by weight of the obtained methylated hydroxypropyl cellulose, a 2 mol% aqueous solution of trifluoroacetic acid 3 was added.
After adding 00 weight and treating at 120 ° C. for 3 hours, the pH was adjusted to 7 using barium carbonate. To this was added 1.5 parts by weight of sodium borohydride, and the mixture was stirred at room temperature for 1 hour, and evaporated to dryness at 100 ° C. 100 parts by weight of acetic anhydride and 200 parts by weight of pyridine were added to the remaining contents,
Treated at 0 ° C. for 3 hours. After cooling, 500 parts by weight of water was added, and the mixture was extracted twice with 50 parts by weight of carbon tetrachloride.
The carbon tetrachloride was evaporated and the residue was subjected to GC analysis. GC
Table 1 shows the results of obtaining the total ratio of polysubstituted compounds having 2 or more hydroxypropyl group substitution moles and the composition ratio of unsubstituted products based on the peak area in the analysis.

(3) The low-substituted hydroxypropylcellulose obtained in solution properties and solid properties is
The low-substituted hydroxypropylcellulose was dissolved in a 10% by weight aqueous sodium hydroxide solution so that the concentration of the low-substituted hydroxypropylcellulose was 2% by weight. The viscosity of a solution prepared by changing the dissolution temperature to 10 ° C., 30 ° C., and 50 ° C. was measured using a B-type viscometer, and the visible light of a blank (water) was measured using a photoelectric colorimeter (5E). The transmittance was measured. Table 1 shows the above measurement results. The alkaline solution of the product showed high transparency over a wide temperature range.

Example 2 100 parts by weight of powdered pulp were immersed in a 45% by weight aqueous solution of sodium hydroxide, and then pressed under pressure to give a weight ratio of cellulose to cellulose of 0.46 and a water content of 0.4. 64 alkaline celluloses were prepared. Production was carried out in the same manner as in Example 1, (1) except that 32 parts by weight of propylene oxide (molar ratio to cellulose: 0.89) was added and the reaction was carried out at 75 to 80 ° C for 2 hours. 112 parts by weight of propylcellulose were obtained. The average number of moles of substituted hydroxypropyl groups was 0.39. The composition and solution properties of the substituted product were determined in the same manner as in Example 1, and the results are shown in Table 1. The alkaline solution of this product showed high transparency over a wide temperature range.

Example 3 100 parts by weight of sheet pulp were immersed in a 25% by weight aqueous sodium hydroxide solution.
By pressurizing and compressing, alkali cellulose having a weight ratio to cellulose of 0.20 of alkali hydroxide and 0.67 of water was prepared. Production was carried out in the same manner as (1) of Example 1 except that 8.7 parts by weight of propylene oxide (molar ratio to cellulose: 0.24) was added and the reaction was carried out at 35 to 40 ° C. for 4 hours. Thus, 103 parts by weight of hydroxypropylcellulose was obtained. The average number of moles of substituted hydroxypropyl groups was 0.11. The composition and solution properties of the substituted product were determined in the same manner as in Example 1, and the results are shown in Table 1. The alkaline solution of this product showed high transparency over a wide temperature range.

(Comparative Example 1) The amount of propylene oxide charged was 45 parts by weight (molar ratio to cellulose: 1.26)
The production was carried out in the same manner as in Example 1, (1) except that
15 parts by weight were obtained. The average number of moles of substituted hydroxypropyl groups was 0.45. The composition and solution properties of the substituted product were determined in the same manner as in Example 1, and the results are shown in Table 1. The alkali solution of the product was cloudy and had low transparency.

(Comparative Example 2) Production was carried out in the same manner as in (1) of Example 1 except that the reaction was carried out at a temperature of 85 to 100 ° C for 1.5 hours. I got The average number of moles of substituted hydroxypropyl groups was 0.24. The composition and solution properties of the substituted product were determined in the same manner as in Example 1, and the results are shown in Table 1. The alkali solution of the product was cloudy and had low transparency.

(Comparative Example 3) 100 parts by weight of sheet pulp was immersed in an 8% by weight aqueous sodium hydroxide solution, and the weight ratio of alkali hydroxide to cellulose was adjusted to 0.0.
8. Production was carried out in the same manner as in Example 2 except that alkali cellulose adjusted to a water content of 1.0 was used to obtain 101 parts by weight of low-substituted hydroxypropylcellulose. The average number of moles of substituted hydroxypropyl groups was 0.06. The composition and solution properties of the substituted product were determined in the same manner as in Example 1, and the results are shown in Table 1. This product hardly dissolved in aqueous sodium hydroxide solution.

[0027]

[Table 1] ¹⁾ "Degree of substitution" was determined using the Zeisel method. “MS” represents the average number of substituted moles. ^{2) As the} “substituted composition”, “unsubstituted” represents a substituted product having 0 hydroxypropyl group substitution moles, and “monosubstituted”
Represents a substituted product having a hydroxypropyl group-substituted mole number of 1, and "polysubstituted" represents a total sum of substituted products having a hydroxypropyl group-substituted mole number of 2 or more. The GC measurement conditions were as follows: Apparatus: 5980 SERIES II GAS CHROM manufactured by Hewlett Packard.
ATOGRAPH column: 5% phenylmethyl silicone 0.2mmφ × 25
m, sample: 1 μl, injector and detector temperature: 250 ° C., oven temperature: heated to 170 to 300 ° C. (heating rate 2.
5 ° C./min). ³⁾ “Solution properties” refers to hydroxypropyl cellulose
It measured using the solution melt | dissolved so that it might become 2 weight% in 0 weight% sodium hydroxide aqueous solution. ^{4) The} "light transmittance" was measured using a photoelectric colorimeter 5E, a 20 mm cell, and visible light. ⁵⁾ “Viscosity” was measured at 10 ° C. using a B-type viscometer.

[0028]

The low-substituted hydroxypropylcellulose of the present invention is excellent in transparency when dissolved in an aqueous alkali solution as compared with conventional low-substituted hydroxypropylcellulose, and its solubility does not change with temperature. Since a stable solution can be provided in a wide temperature range, it can be used in various applications as a thickener for an alkaline aqueous solution. I will provide a.

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[Procedure amendment]

[Submission date] April 30, 1999 (1999.4.3)
0)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0028

[Correction method] Change

[Correction contents]

[0028]

The low-substituted hydroxypropylcellulose of the present invention is excellent in transparency when dissolved in an aqueous alkali solution as compared with conventional low-substituted hydroxypropylcellulose, and its solubility does not change with temperature. Since a stable solution can be provided in a wide temperature range, it can be used in various applications as a thickener for an alkaline aqueous solution.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Sakae Ohara 28, Nishifukushima, Oku-ku, Kutsugi-mura, Nakakibijo-gun, Niigata Prefecture F-term in Shin-Etsu Chemical Co., Ltd. Synthetic Technology Research Laboratory 4J002 AB031 GB04

Claims (1)

[Claims] 1. A low-substituted hydroxypropyl cellulose having an average number of moles of substituted hydroxypropyl groups per glucose unit of 0.1 to 0.4, the number of glucose units substituted with 2 moles or more of hydroxypropyl groups. Is less than 5% of the total number of glucose units,
And the low-substituted hydroxypropylcellulose is
90% light transmittance at 10 ° C. to 50 ° C. in a solution dissolved at a concentration of 2% by weight in a 0% by weight aqueous sodium hydroxide solution
The low-substituted hydroxypropylcellulose described above.