JPH08245701A - Highly transparent hydroxyalkyl cellulose and its production - Google Patents

Abstract

PURPOSE: To obtain the subject highly transparent and high-quality compound by acetylating a raw cellulose in a high concentration solution of an alkali metal hydroxide, partly neutralizing a part of the alkali in the reactional system, and then conducting an etherification. CONSTITUTION: First, a raw cellulose is dispersed in a mixed solution of water and a hydrophilic organic solvent (pref. t-butanol) containing 1.5-2mol, per glucose unit of the cellulose, of an alkali metal hydroxide. Secondly, a part of the alkali metal hydroxide in the system (pref. 0.3-0.7mol, per glucose unit of the cellulose) is neutralized. Finally, the resultant cellulose is etherified to obtain the objective compound. The etherifying agent is e.g. ethylene oxide, propylene oxide. As for this compound, when the substitution degree reaches >=1.4, a 1% aqueous solution thereof presents a transparency of >=600mm, therefore being preferable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydroxyalkyl cellulose, which is extremely effective as a base material for paints, dispersants, cosmetics and the like, and various mixed ethers, and a method for producing the same.

[0002]

2. Description of the Related Art Regarding the production of cellulose ethers, especially hydroxyalkyl cellulose, there are numerous descriptions due to their versatility and usefulness. However, the basic technology is lower aliphatic alcohols such as isopropyl alcohol (IPA) and tertiary butanol (TBA),
Water, in a mixed solution of alkali metal hydroxide, a cellulose raw material in a slurry state is treated with an equimolar or a slight excess of alkali metal hydroxide to make alkali cellulose, and then an etherifying agent is added to the cellulose ether. Is generally obtained.

Here, the pretreatment with an alkali metal hydroxide is a kind of activation treatment called alcelization or mercerization. In this pretreatment, it is generally said that the hydroxyl groups in cellulose are in an alcoholate state, but the details are unknown. However, this treatment changes the crystal structure of the cellulose itself, and the crystal structure changes depending on the alkali concentration.
It is known to change from type II, type III, and type IV.

In the actual production of hydroxyalkyl cellulose, this pretreatment with alkali is not merely activation. That is, the charged cellulose raw material is obtained in the form of a sheet, but at the manufacturing site, from the viewpoint of the size of the reactor, the economical efficiency and the process,
It is general that the sheet-shaped cellulose is cut and put into a reaction system in a powder state. However, at this time, the cellulose fiber itself is damaged by crushing, the cut part is crushed, the penetration of the chemical solution is hindered, and further the moisture in the molecule disappears due to friction heat, and the intramolecular hydrogen bond is generated. It has been pointed out that the reactivity is extremely deteriorated due to the occurrence of. In one aspect, the pretreatment with alkali is performed to remove these deterioration factors.

Generally, the swelling of cellulose with an aqueous alkaline solution is extremely good, and therefore the swelling effect is greater when treated with a high-concentration alkali.

[0006]

However, when treated with a high-concentration alkali, it is good in terms of regeneration of the deteriorated portion and swelling activation treatment, but side reactions become severe during the etherification, and the etherification agent The utilization rate of will be significantly reduced and it will not be economical. Therefore, in the conventional etherification reaction, the alkali concentration in the mercerization step is generally about 1.0 to 1.4 mol per glucose unit.

However, unless the pulp is crushed sufficiently mildly, for example, if it is disintegrated in water, the swelling in mercerization is insufficient, so the degree of substitution of the ether group must be 2.0 or more. However, when it is made into an aqueous solution, it is difficult to obtain one having excellent transparency.

[0008]

Means for Solving the Problems The present inventor originally intended to activate crushed, cut and deteriorated cellulose raw materials,
In order to obtain a cellulose ether having good properties, based on the idea that it is preferable to carry out a high-concentration alkali treatment in the stage of alcelization, as a result of diligent study, when etherifying the raw material cellulose, a hydrophilic organic solvent Pretreatment with a mixed solution of water and alkali metal hydroxide in an amount of 1.5 to 2.0 mol per glucose unit of cellulose, and prior to etherification, part of the alkali metal hydroxide is neutralized and then etherified. We have found a method for producing cellulose ethers. Furthermore, the hydroxyalkyl cellulose obtained by this method was found to be extremely excellent in the transparency of the aqueous solution as compared with the one having the same degree of substitution obtained by the conventional method, and completed the present invention.

That is, in the present invention, the raw material cellulose is mixed with a hydrophilic organic solvent and water containing 1.5 to 2.0 mol of alkali metal hydroxide per glucose unit (hereinafter simply referred to as glucose unit) of the cellulose. And then neutralizing a part of the alkali metal hydroxide in the system, and then etherifying the cellulose, and a hydroxyalkyl cellulose produced by this method. It provides cellulose.

The cellulose raw material in the present invention may be either pulp or linter. Further, generally, a sheet-shaped material is used after dry crushing and cutting, but a fluff-shaped material or a block-shaped material is also applicable.

As the alkali used in the pretreatment with alkali in the present invention, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, or alkaline earth metal hydroxides such as calcium hydroxide and magnesium hydroxide are used. To be These may be used as an aqueous solution having an appropriate concentration. The general mercerization process temperature is 15
It is carried out at a temperature of not more than 0 ° C., but the same method is used in the present invention. After adding the alkali metal hydroxide,
The reaction is allowed to proceed by leaving it at a predetermined temperature for an appropriate time, for example, about 60 to 120 minutes.

The production method of the present invention includes a step of neutralizing a part of the alkali metal hydroxide before the etherification, but the neutralizing agent at that time is not particularly limited, and an organic acid such as acetic acid is used. , And inorganic acids such as nitric acid can be used.

Generally, the etherification of cellulose is carried out in a slurry state, and the dispersion medium used in that case is a hydrophilic organic solvent such as isopropyl alcohol or a lower alcohol such as tertiary butanol, and water. It is a mixed solution. The hydrophilic organic solvent concentration in the mixed solution is preferably 88 to 92% by weight. Further, as the hydrophilic organic solvent, tertiary butanol is particularly preferable. The water may be derived from the alkali metal hydroxide aqueous solution.

Regarding the reaction method of etherification, in the present invention, as described above, after the treatment with an alkali of 1.5 to 2.0 mol / glucose unit in the case of the alcelization, 0.3 to 0.7 mol / glucose is added before adding the etherifying agent. The unit of alkali is neutralized for etherification. Generally, a method of reacting at a temperature near the boiling point of the etherifying agent for a certain period of time is adopted.
Any etherifying agent may be used as long as it can obtain the intended hydroxyalkyl cellulose, and examples thereof include ethylene oxide, propylene oxide, and butylene oxide. Of course, an etherification reaction using an etherifying agent other than this may be used.

The obtained reaction product can be washed with a mixed solution of a hydrophilic organic solvent and water to remove salts produced by neutralization, and dried to obtain the target cellulose ether.

The hydroxyalkyl cellulose thus obtained has a degree of substitution of about 1.1 to 1.9, but has a very good solubility in water, and the hydroxyalkyl cellulose having the same degree of substitution obtained by a general method. Shows better transparency than In particular, those having a degree of substitution of 1.4 or more have further improved transparency, and a 1% aqueous solution has a transparency of 600 mm or more.

The reason for this is not clear, but it is presumed that the treatment with a high-concentration alkali gives a hydroxyalkyl cellulose having a distribution of substituents with a very long chain. In general, the mechanism by which hydroxyalkyl cellulose is dissolved in water is not that it is dissolved as a polyelectrolyte like carboxymethyl cellulose, but because hydroxyalkyl groups are bonded, the crystalline structure of cellulose is It is said to dissolve when it is disintegrated. From this viewpoint, it is speculated that the hydroxyalkyl cellulose obtained by the present invention has a long-chain substituent, and therefore exhibits good water solubility even if the degree of substitution is relatively low. . In the present invention, the term “transparency” means that obtained by the method described in Examples below.

The hydroxyalkyl cellulose of the present invention thus obtained is specifically hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxybutyl cellulose or the like having various substitution degrees.

[0019]

EXAMPLES The present invention will now be described by way of examples, which should not be construed as limiting the scope of the present invention.

(Measurement Method of Transparency) An aqueous solution is prepared by dissolving 1% by weight of hydroxyalkyl cellulose obtained by the reaction in water. On the other hand, diameter 30mm, height 7
00mm one side open glass tube and 1mm thick straight line 1mm
Prepare two papers drawn at intervals. Stick a straight line on the closed part (bottom) of the glass tube, turn on a 40W fluorescent lamp in a dark room, and illuminate the top 20 cm of the glass tube toward the bottom. Stand the glass tube vertically, put the prepared aqueous solution in such a way that air bubbles do not enter, and display the height at which the distance between the two straight lines cannot be seen as transparency (mm).

Example 1 20 g (pure content) of pulp crushed with a cutter mill was placed in a separable flask and dispersed in 180 g of t-butanol, and then 8.4 g of caustic soda (1.7 mol / glucose unit) was dissolved in 20 g of water. Add caustic soda solution at 15 ℃
After performing alcelization for 120 minutes, acetic acid was added to the mixture at 15 ° C over about 2 minutes, and the amount of residual caustic soda was 1.3 mol per glucose unit (that is, the neutralization amount was 0.4 mol). I went to sum. At this time, the temperature in the reaction system rises slightly due to the heat of neutralization, but stirring is performed for 10 minutes in this state in order to uniformly perform the neutralization. In the meantime, cool and adjust the system so that the temperature becomes 15 ° C. 3.7 mol of ethylene oxide per glucose unit was added to the obtained slurry of alcerized pulp, and the temperature was raised to 50 ° C. for 90 minutes, and further raised to 70 ° C. for 90 minutes for reaction. The hydroxyethyl cellulose obtained had a degree of substitution of 1.68 and a transparency of a 1% aqueous solution of 640 mm or more.

Example 2 In the same manner as in Example 1, 2.0 mol of caustic soda per glucose unit was treated at the stage of alcerization, and the amount of residual caustic soda was 1.3 per glucose unit before etherification.
The reaction was carried out by neutralizing to a molar amount (that is, a neutralization amount of 0.7 mol). The degree of substitution of the obtained hydroxyethyl cellulose was 1.86, and the transparency of a 1% aqueous solution was 640 mm or more.

Example 3 In the same manner as in Example 1, the mixture was treated with 1.7 mol of caustic soda per glucose unit at the stage of alcerization, and the amount of residual caustic soda was 1.3 per glucose unit before etherification.
It neutralized so that it might become a mol (namely, the amount of neutralization is 0.4 mol).
Further, the reaction was carried out so that the amount of ethylene oxide added to the reaction system was 2.0 mol per glucose unit. Substitution degree of the obtained hydroxyethyl cellulose is 1.5
The transparency of the 0% 1% aqueous solution was 640 mm or more.

Comparative Example 1 The reaction was carried out in the same procedure as in Example 1, but the amount of caustic soda in the system was 1.3 mol per glucose unit through the process of alcelization and etherification. The degree of substitution of the obtained hydroxyethyl cellulose is 1.94, and the transparency of a 1% aqueous solution is 1
It was 20 mm.

Comparative Example 2 The reaction was carried out by the same procedure as in Example 1, but the amount of caustic soda in the system was 1.3 mol per glucose unit through the addition of alcel and etherification, and the added ethylene oxide was 1.5 mol per glucose unit. Mole. The degree of substitution of the obtained hydroxyethyl cellulose was 1.45, and the transparency of a 1% aqueous solution was 85 mm.

Comparative Example 3 The reaction was carried out in the same procedure as in Example 1, except that the amount of caustic soda at the time of alcelization was 1.8 mol per glucose unit, and the amount of residual caustic soda was changed per glucose unit before the etherification reaction. The solution was neutralized with acetic acid to 1.0 mol (that is, the neutralization amount was 0.8 mol). The hydroxyethyl cellulose thus obtained had a hydroxyethyl substitution degree of 1.91 and was 1
% Aqueous solution had a transparency of 500 mm.

Comparative Example 4 The reaction was carried out in the same procedure as in Example 1, except that the amount of caustic soda at the time of alcelization was 1.5 mol per glucose unit, and the treatment was carried out so that the residual caustic soda was 1.3 mol per glucose unit before the etherification reaction. (Ie neutralization amount is 0.2 mol)
It was neutralized with acetic acid. The hydroxyethyl cellulose thus obtained had a hydroxyethyl substitution degree of 1.96 and a 1% aqueous solution had a transparency of 25 mm.

Comparative Example 5 The reaction was carried out in the same procedure as in Example 1, but the etherification was carried out without neutralization after the alcelization. The degree of substitution of the obtained hydroxyethyl cellulose is 1.72, and the transparency of a 1% aqueous solution is
It was 260 mm.

Claims (7)

[Claims] 1. A raw material cellulose is dispersed in a mixed solution of a hydrophilic organic solvent containing 1.5 to 2.0 mol of an alkali metal hydroxide per glucose unit of the cellulose and water, and then the alkali metal hydroxide in the system is dispersed. A method for producing a hydroxyalkyl cellulose, which comprises neutralizing a part of a product and then etherifying the cellulose. 2. The hydrophilic organic solvent concentration in the mixed solution is
The method for producing a hydroxyalkyl cellulose according to claim 1, which is 88 to 92% by weight. 3. The method for producing a hydroxyalkyl cellulose according to claim 1, wherein the alkali metal hydroxide in the system is neutralized by 0.3 to 0.7 mol per glucose unit of cellulose before etherification. 4. The method for producing hydroxyalkyl cellulose according to claim 1, wherein the hydrophilic organic solvent is tertiary butanol. 5. The method according to any one of claims 1 to 4, wherein the hydroxyalkyl substitution degree is 1.1 to 1.
A hydroxyalkyl cellulose that is 9. 6. A hydroxyalkyl cellulose produced by the production method according to claim 1. 7. The hydroxyalkyl substitution degree is 1.4 to 1.9.
A hydroxyalkyl cellulose whose 1% aqueous solution has a transparency of 600 mm or more.